Nozzle geometry terminology:\nIf the flow area increases continuously from the inlet to the outlet, how is such a steam nozzle classified?

Introduction / Context:
Nozzles are classified by how their cross-sectional area changes along the flow direction. The geometry dictates whether subsonic or supersonic acceleration occurs and where choking is possible. Correct naming avoids confusion in turbine and jet calculations.

Given Data / Assumptions:

• Cross-sectional area increases monotonically from inlet to outlet.
• Working fluid is steam, but terminology is general.
• Flow regime depends on inlet state and pressure ratio.

Concept / Approach:
A nozzle with monotonically increasing area is a divergent nozzle. In compressible flow, a purely divergent duct decelerates subsonic flow but accelerates supersonic flow. Choking and acceleration from subsonic to supersonic require a convergent–divergent (C–D) shape (De Laval nozzle), not a purely divergent or convergent one.

Step-by-Step Solution:

Verification / Alternative check:
Classical area–Mach number relations show that dA > 0 accelerates M > 1 flow and decelerates M < 1 flow, consistent with the naming and applications.

Why Other Options Are Wrong:

• Convergent: Area decreases.
• Convergent–divergent: Area first decreases to a throat, then increases.
• None of these: Incorrect because “divergent nozzle” precisely matches.

Common Pitfalls:
Assuming any divergent passage yields supersonic speeds; without a throat and sufficient pressure ratio, the flow may remain subsonic and decelerate.

Final Answer:
divergent nozzle